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Jun 16, 2018
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hello all,
my 74 mk2a has vernia type ajusters front and rear and a comstock (or similar) head steady , the front and rear have the series of holes in the adjuster with which to insert a tool to adjust ,
i have blocked the bike up on the frame tubes as instructed , slackened off thru bolt a couple of turns and tightened up adjuster to its stop then backed off 1 and a 1/2 holes , this i'm told gives me the required measurement , this i also did on the rear mount , so whats the problem i hear you all ?, NO change at all ! , i am still looking for this magical vibe free zone above 3000 revs , is this the correct procedure , if it is should i look at removing the iso to inspect / regrease the rubbers ? , also is the rear mount adjusted by the same amount ?, any info welcome ,
thanks Colin
Oh boy. Did you put in a feeler gauge to see where the clearance is? What happens if you back it off a bit more?
There has been talk on list about iso rubber hardness in the past. I think RGM offers or offered softer rubbers
but they may only be for the build up earlier typs not the bonded one piece affair.
My 1972 stock from the factory had less vibes than my current 850 with the once piece iso and verniers.
Below 2800 it is pretty rough. A grand higher it is much smoother but I noticed yesterday that it also seems to
depend on throttle setting.
Try backing off and testing.
Are your Thrust washers greased up in the Iso's ? 06-4748.
Did you re-tighten the front bolt and rear stud to the correct torque values ? 30 lbs. each.
1 1/2 turns out will achieve .006 Inch clearance that will allow things to bounce about up and down freely but it's only a manual recommendation in actuality.
My verniers seem happiest at .008 or even .010 play after tightening up the 2 units.
Mind you racer types like less clearance to improve handling in corners.
Try opening up the gaps a tad and report back to us ?
There is a series of You Tube videos which will answer all of your questions about isolastics. I too experienced what you describe and
only could achieve a relatively vibration free ride above 3000 by increasing the space (loosening the adjusters). beyond the recommendation.

The "back off by 1 1/2 holes" method can be unreliable.

I suggest you use a feeler gauge and always check clearance after the Iso. bolt (front) or stud (rear) has been fully tightened as play in the adjuster threads often results in a loss of clearance from the tightening of the bolt/stud.

I recommend you insert the required thickness feeler gauge, tighten the adjuster until the feeler just slides freely, then tighten the Iso. bolt/stud in stages checking the feeler still slides. If the feeler becomes tight then loosen the bolt/stud and back off the adjuster. Continue to do this until the feeler slides with the Iso. bolt/stud fully tightened.
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My early bike was really smooth when I first got it (72) and it certainly handled light years better than the top heavy CB450 I sold. When I replaced the iso's from stuff I bought at OB (2008), the vibration level went up. I tried everything with the Hemming adjusters and nothing changed it much, especially below 3K no matter what spacing I used except tight or completely loose. Above 3K it's OK enough. I finally put the engine spring on the front of the engine to the frame, but all that did was reduce the idle vibrations quite a bit. Did nothing for 3K and up. I still get a little buzz in the pegs at speed. 19 tooth sprocket. I'm thinking the new rubbers are a bit more solid for better handling. But unless someone has scientifically measured the compression of the original iso rubbers and compared them to the new ones, who's to know? I think Atlantic Dave did some comparisons of the newer ones, 850/750 but don't quote me on that.
The problem, IMO, with any "fixed" adjustment -whether it's number-of-turns or a feeler gauge thickness - is that it might work well on one bike but not another. IOW, the only way to get it like you want it is to try different settings and ride the bike. I found that on my '73, with brand new rubbers and the OEM shim system on the front and a vernier on the rear, the best setting is .006. One obvious issue is that the setting for least vibration and the setting for best handling tend to be at opposite ends. But I found that I couldn't tell any handling difference between .006 and 0. I'm not saying that NO ONE could tell the difference - just that I couldn't. OTOH, the vibration at 0 is not a acceptable at all. .010 felt noticeably "looser" to me handling-wise though the engine vibration was handled quite well. I get some juddering in the front wheel/forks at a stop at idle, much more noticeable with the front brake engaged and some vibration up to around 2800RPM but it's quite smooth at any higher RPM.

.006 produces the best combination for me/my riding. But obviously this might change with a different set of iso rubbers and/or a different riding style.
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